Affiliations: Department of Experimental Medicine and Biotechnology,
Postgraduate Institute of Medical Education and Research, Chandigarh,
India | Department of Biochemistry, Panjab University,
Chandigarh, India
Note: [] Corresponding author: Safrun Mahmood, Geneticist, Department of
Experimental Medicine and Biotechnology, Postgraduate Institute of Medical
Education and Research, Chandigarh, 160012, India. Tel.: +91 172 2755237; Fax:
+91 172 2744401; E-mail: mahmoodpgi@gmail.com
Abstract: Adult-type hypolactasia is an autosomal recessive condition
resulting from the physiological decline of the lactase enzyme activity in
intestinal cells which occurs in a significant proportion of the global
population. Mechanisms proposed to explain the occurrence of adult-type
hypolactasia include: (a) decreased production of lactase, (b) synthesis of an
inactive high molecular weight lactase, (c) defective post-translational
modifications, and (d) susceptibility of lactase to luminal proteases during
weaning due to change in levels of sialylated and fucosylated enzymes in the
small intestine. Recently, the C/T-13910 polymorphism on chromosome 2q21 in
North-European populations has been found to be associated with lactase
activity and its genetic typing is advocated as a first-stage screening test
for adult hypolactasia. Available biochemical methods for diagnosis of
adult-type hypolactasia consists of the lactose tolerance test (LTT), which
measures the increase in blood glucose after an oral lactose load, and the
hydrogen breath test (HBT), that is based on the determination of exhaled
hydrogen produced by the bacterial flora in the colon after an oral lactose
load. These methods require significant procedural time both for the patient
and the processing clinical laboratory. The present review describes genetic
regulation of lactase expression and various single nucleotide polymorphisms
(SNPs) associated with adult-type hypolactasia and lactase persistence in
different human populations.
